1. Field of the Invention
The present invention relates to an apparatus for controlling the pressure of braking fluid and more particularly to the apparatus preferably used to control the pressure of the braking fluid such as in an anti-lock control or a traction control. The present invention relates in particular to a construction for installing a solenoid valve, to be used to reduce, maintain or pressurize the braking fluid, on a housing so as to make the apparatus compact and reduce manufacturing cost.
2. Description of Background Information
An example of a conventional apparatus for controlling the pressure of the braking fluid is described below with reference to FIG. 6.
The apparatus for controlling the pressure of the braking fluid is installed in a circuit for controlling the pressure of the braking fluid. A pressure receiving portion 4a of a frame 4 of a solenoid valve 3 is fluid-tightly inserted into a mounting opening 2 formed in a housing 1.
In the frame 4, a cylindrical portion 4b is formed in continuation with the pressure receiving portion 4a, and a valve chest 5 and a hollow portion 6 are formed inside the cylindrical portion 4b. There are provided, on the pressure receiving portion 4a of the frame 4, a fluid flowing path 8 connecting the valve chest 5 with a pressurizing duct 7 with each other and a discharge path 10 connecting the valve chest 5 with a discharge duct 9 with each other.
As shown in detail in FIG. 6, an armature 12 is axially slidably mounted in the hollow portion 6, and a fixed valve seat 14 mounted on the fluid flowing path 8 is opened and closed by a movable valve ball 13 fixed to the armature 12. The frame 4 incorporates a stator 16 in opposition to the armature 12, and a cylindrical electromagnetic coil 17 is installed on the periphery of the stator 16.
A plate-shaped holding member 18 is disposed on the stator of the solenoid valve 3. The solenoid valve 3 is pressed against the housing 1 by the holding member 18 and thus the solenoid valve 3 is held by the housing 1 against hydraulic pressure acting on the pressure receiving portion 4a.
That is, a plurality of inserting openings 18a are provided through the holding member 18, and screw openings 1a are formed in the housing in correspondence with the inserting openings 18a so that a bolt 20 inserted through the inserting opening 18a and a sleeve 19 is screwed into the screw opening 1a. In this manner, the holding member 18 presses the solenoid valve 3 strongly against the housing 1, thus holding the solenoid valve 3.
In the solenoid valve 3, when the electromagnetic coil 17 is energized, as shown by a two-dot chain line of FIG. 6, there is formed a magnetic circuit constituting a magnetic path in the order of the cylindrical portion 16a of the stator 16, the armature 12, the cylindrical portion 4b of the frame 4, and the flanged portion 16b of the stator 16. The magnetic force generated by the magnetic circuit moves the armature 12 toward the valve-open side against the urging force of a spring 18.
In the conventional apparatus as shown in FIG. 6, however, it is necessary to provide the holding member 18 so as to mount the solenoid valve 3 in the housing 1. As a result, the dimension of the solenoid valve 3 becomes larger in its axial direction by the thickness of the holding member 18 as shown by an arrow (A). Thus, the apparatus becomes larger by the dimension.
Another example of an apparatus for controlling the pressure of braking fluid is described below with reference to FIG. 7. In this apparatus, a male screw 4c is formed in the periphery of the pressure receiving portion 4a of the frame 4, and a female screw 2c is formed on the mounting opening 2 in correspondence with the male screw 4c. The solenoid valve 3 is fixed to the housing 1 by the engagement between the male screw 4c and the female screw 2a. In this construction, the dimension of the solenoid valve 3 can be reduced in its axial direction because it is unnecessary to provide the holding member unlike the conventional apparatus as shown in FIGS. 6 and 8.
In the above-described construction, however, the apparatus becomes large in the direction in which the solenoid valves 3 are arranged because it is necessary to provide a certain interval between adjacent solenoid valves 3 in consideration of mechanical strength thereof.
That is, it is necessary to make the interval (thickness (B) of screw thread cutting portion) between the male screws 4c of the adjacent solenoid valves 3 five times as large as the height of the male screw 4c in order to secure strength.
In the conventional apparatus as shown in FIG. 7, there is a possibility that foreign matter discharged from the male screw 4c penetrates into the valve chest 5 in assembling the apparatus although the valve chest 5 has a construction for preventing the foreign matter from penetrating thereinto. The penetration of the foreign matter into the valve chest 5 causes a big problem. Accordingly, it is difficult to adopt the construction as shown in FIG. 7.
The conventional apparatuses as shown in FIGS. 6 and 7 have problems in manufacturing cost.
That is, it is necessary to provide the fluid flowing path 8 and the discharge path 10 in the frame 4. To this end, it is necessary to machine them from a solid material. But a large quantity of material is cut off and bored to form the valve chest 5 and the hollow portion 6 in the cylindrical portion 4b. Therefore, the apparatus is manufactured at a high cost.